The .mtx files are multiple (tga?) image files compiled into 1 file as the bat files say. Given the license agreement and the unobscured nature of the files, someone should email the collective and ask if they could dole out some file specs or even the mtx.exe that they used to compile the 'MULTITEX' files. Its highly unlikely that you'd get a helpful response but its worth eliminating the simple before working out the file specs.